Drawing an arrow over my plot

[Joey Mukherjee]

I have a plot of data with a box around it and all is well.

However, I want to draw an arrow going through the middle of the plot from edge 
to edge given two points. 

What is the best way of accomplishing this?  I tried creating a polydata on my 
own and rendering that however, the arrow never shows up.  My guess is it is 
buried within my plot so I can't see it.

Has anyone else done this?

Thanks,
Joey

+--------------------------------------------------------------------------+
+     Joey Mukherjee                     "I am amused by the simplicity    +
+      joey at swri.org                      of this game.  Bring me your     +
+  http://www.space.swri.edu/~joey        finest meats and cheeses."       + 
+                                                                          +
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